US5173693A - Position encoder using a pseudo-random coding sequence - Google Patents

Position encoder using a pseudo-random coding sequence Download PDF

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Publication number
US5173693A
US5173693A US07/536,678 US53667890A US5173693A US 5173693 A US5173693 A US 5173693A US 53667890 A US53667890 A US 53667890A US 5173693 A US5173693 A US 5173693A
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sequence
tuple
bits
fragments
carrier element
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US07/536,678
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English (en)
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Richard L. Fry
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Dr Johannes Heidenhain GmbH
Haseltine Lake and Co
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Haseltine Lake and Co
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Assigned to TECHNOLOGY PARTNERSHIP LIMITED, THE, A BRITISH CO. reassignment TECHNOLOGY PARTNERSHIP LIMITED, THE, A BRITISH CO. ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: FRY, RICHARD L.
Assigned to DR. JOHANNES HEIDENHAIN GMBH reassignment DR. JOHANNES HEIDENHAIN GMBH ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: TECHNOLOGY PARTNERSHIP LIMITED, THE, A BRITISH CO.
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M1/00—Analogue/digital conversion; Digital/analogue conversion
    • H03M1/12—Analogue/digital converters
    • H03M1/22—Analogue/digital converters pattern-reading type
    • H03M1/24—Analogue/digital converters pattern-reading type using relatively movable reader and disc or strip
    • H03M1/28—Analogue/digital converters pattern-reading type using relatively movable reader and disc or strip with non-weighted coding
    • H03M1/282—Analogue/digital converters pattern-reading type using relatively movable reader and disc or strip with non-weighted coding of the pattern-shifting type, e.g. pseudo-random chain code
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/244—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing characteristics of pulses or pulse trains; generating pulses or pulse trains
    • G01D5/249—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing characteristics of pulses or pulse trains; generating pulses or pulse trains using pulse code
    • G01D5/2492—Pulse stream
    • G01D5/2495—Pseudo-random code
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03M—CODING; DECODING; CODE CONVERSION IN GENERAL
    • H03M7/00—Conversion of a code where information is represented by a given sequence or number of digits to a code where the same, similar or subset of information is represented by a different sequence or number of digits
    • H03M7/26—Conversion to or from stochastic codes

Definitions

  • This invention relates to the decoding of random or pseudo-random sequences and is applicable, for example, to absolute position encoders.
  • An m-sequence is a sequence of 2 n -1 bits so arranged that all of the n-tuple groups of successive bits are unique. If the sequence is considered to be circular, there are then 2 n -1 unique n-tuples. The bit pattern of each n-tuple thus defines its position in the m-sequence. It is thus possible to make an absolute encoder in which the limit of physical resolution is one bit of the m-sequence. This is particularly useful for optical and high precision encoders where the physical resolution precludes the use of more than a single optical track.
  • the invention involves interleaving fragments, e.g. two fragments, of the same maximal length sequence, where the fragments have lengths with no common factors.
  • a device having a sequence of bits characterised in that said sequence of bits comprises a plurality of different interleaved fragments of a single maximal length sequence, said fragments having lengths with no common factors such that there exists integer x whereby any x-tuple of x successive bits of the sequence of bits defines an absolute location in the sequence.
  • a device having a sequence of machine readable bits characterised in that, for a given integer x, in any x-tuple of x successive bits of said sequence, different bits of the x-tuple form a set of y-tuples together uniquely defining the position of the x-tuple in the sequence, each x-tuple being unique but each y-tuple occurring more than once in different x-tuples.
  • FIG. 1 shows an interleaved pseudo random code
  • FIG. 2 shows a circuit arrangement for decoding the code of FIG. 1
  • FIG. 3 shows an encoder arrangement embodying the present invention
  • FIG. 4A shows an interleaved code
  • FIG. 4B shows a Moire track
  • FIG. 4C shows a Moire signal resulting from the Moire track of FIG. 4B
  • FIG. 5 shows an optical arrangement of FIG. 3
  • FIG. 6 shows a flowchart for a microprocessor of the arrangement of FIG. 3.
  • this example uses an m-sequence of order (20/2)+1, i.e. 11 (i.e. 2047 bits long).
  • This sequence is broken into two fragments of length 1024 and 1023. Note that each 11-tuple still appears only once in the sequence and only in the A or B fragment, never both. Any m-sequence can be broken into two such fragments with a length difference of 1, but the exact position in which it can be broken while preserving the required properties is best found by exhaustive searching using a computer.
  • each fragment is repeated an appropriate number of times.
  • the bit sequence of the encoder is as shown in FIG. 1.
  • a decoder would need to have some way of determining the phase of the two streams.
  • a decoder itself can determine the phase by seeing from which fragment A or B a particular 11-tuple has come.
  • FIG. 2 A practical implementation of this is shown in FIG. 2. Again for illustration an encoder with two fragments of an 11 bit code is used.
  • the 22 bit code sequence is presented from a reading (optical) head to a first-in-first out shift register 1 of decoder electronics and the two interleaved 11 bit fragments extracted and presented to look up table ROMs 2. (These could be replaced by a counter scheme as mentioned earlier, or by a single ROM multiplexed between the two streams and latched).
  • the ROM outputs define which fragment the 11-tuples come from (A or B) and their absolute positions within the fragments.
  • a multiplexer 3 channels the A and B counts to A and B count outputs 4 and 5 and provides a further output Q defining the fragment from which bit 0 of the shift register comes.
  • a simple arithmetic operation is then performed by arithmetic unit 6 to generate the absolute position (count) of the 22-tuple based on the fact that the A fragments precess relative to the B fragments.
  • A' and B' designate the counts, or positions, found within the A and B fragments and A and B represent the lengths of the A and B fragments respectively.
  • the 1M ⁇ 20 bit memory is now reduced to 2 ⁇ 2K ⁇ 11 bit memories 2 and some logic.
  • the technique can be applied to any length of sequence although the longer the sequence the greater the benefit.
  • the system 10 comprises a movement control system 12 together with an optical encoder arrangement 14 based on the principles described above.
  • the numerical tool movement control system includes a translation table 16 mounted on guides to be movable in the x-direction (right to left in FIG. 3).
  • the table 16 carries a nut 18 which threadably engages a rotatable, linear, lead screw 20.
  • a stepper motor 22 is coupled to drive the lead screw 20 and is controlled, via a stepper amplifier 24, by pulses emitted from a microprocessor 26.
  • the translation table 16 supports a linear Moire strip 28, the tracks of which are formed by alternate black and white areas as shown in FIG. 4B. These tracks are read by a stationary Moire reader 30, of known construction, which sends a Moire signal, as shown in FIG. 4C, to a counter 32 and also directly to the microprocessor 26.
  • a counter value output 34 and a counter reset input 36 are coupled to the microprocessor 26.
  • the position of the table 16 is approximately known as a program in the microprocessor 26 caused a desired, known number of pulses to be sent to the stepper motor 22, the number of these pulses corresponding to the desired distance to be moved.
  • the Moire signal produced by the reader 30 from the Moire track is sent to the counter 32.
  • the counter 32 is incremented on every positive-going transition of the Moire signal and thus provides a check on the distance moved.
  • the resulting system is thus a conventional closed-loop movement control system for computer control of the table 16.
  • the translation table 16 supports a chrome on glass strip 38 carrying a pseudo random code (PRC) such as discussed hereinbefore.
  • PRC pseudo random code
  • the code is in the form of a continuous sequence of bits, each bit being represented either by the absence ("0") or presence ("1") of a chrome zone.
  • FIG. 4A illustrates, by different shading, the two zones occupied by the bits of the two interleaved fragments of a single m-sequence, with zones a,c,e etc. representing one fragment and zones b,d,f etc, the other fragment.
  • An optical reading arrangement 39 for scanning the PRC strip 38 will now be discussed with reference to FIG. 5.
  • the arrangement is supported in a case 40 having a light absorbing lining and comprises an LED 42, a photosensitive detector 44, a slit 46 providing an optical aperture for the detector, a cube beam splitter 48 (i.e. two 45 degree prisms arranged to form a cube and having a metal or dielectric coating at their interface 50), a cylindrical lens 52 and a convex lens 54.
  • Light emitted by the LED 42 is reflected by the beam splitter 48 in the direction towards the cylindrical and convex lenses, 52 and 54 respectively. This light is focused by the lenses 52 and 54 onto the strip 38.
  • the optical arrangment remains fixed whilst the PRC strip 38 moves relative to it and the arrangement is constructed so that light from the LED 42 is focused on to one bit at a time to cause an image of that single bit to be formed at the detector 44. It is alternatively possible to read several bits of the code at once by, for example, using an array of detectors.
  • the detector 44 is coupled to the microprocessor 26 via a signal amplifier 56 and the bit value detected is read into a memory of the microprocessor 26 on every positive-going transition of the Moire signal, this point coinciding with the reading of the bit at substantially its mid-point. It is obviously advantageous but not essential to read the code bit at the mid-point of the information so that the contrast is at its highest value and the signal to noise ratio is at its highest value.
  • the device has 18 bits resolution and thus has to read twenty bits of the PRC before it is able to identify the absolute position.
  • each subsequent code bit read after the first twenty identifies with the nineteen immediately preceding bits a new absolute position.
  • the PRC is thus generated by interleaving two fragments of a maximal sequence of length 2.sup.(18/2+1) -1.
  • Each subsequent code bit read after the first twenty identifies with the nineteen immediately preceding bits a new absolute position.
  • Software in the microprocessor 26 thus acts on the bits as would a twenty bit, first-in, first-out, shift register.
  • the microprocessor software causes the steps as shown in the flow chart of FIG. 6 to be carried out.
  • the first step of the software is to initialise the system, including setting the counter 32 to zero and obtaining a value for the desired position P D for the table 16.
  • This position P D can be achieved roughly by sending a determinable number of pulses to the stepper motor 22.
  • the microprocessor 26 calculates the number of pulses X required to attain position P D and starts sending the pulses to the stepper motor 22.
  • the driving screw 20 then starts rotating causing the nut 18 and hence the translation table 16 to move.
  • the reader 30 scans the Moire track to produced the Moire signal and the optical arrangement 39 starts to read the bits of the PRC.
  • the software checks for a leading edge of the Moire signal.
  • the software detects a leading edge of the signal it stores the read value of the PRC bit in memory, the software simulating a first-in, first-out, 20 bit shift register. The leading edge also causes the counter 32 to increment by one.
  • the microprocessor 26 compares the count in the counter with X. If the two values are not close then the software goes back to the step of looking at the Moire signal. If the value in the counter is close to X, then the microprocessor 26 reads the 20 bit pattern in memory, referred to hereinafter as the DEword.
  • the DEword is de-interleaved to get the required two ten bit words referred to as the Dword and the Eword.
  • the respective positions of the Dword in the two fragments A and B are found by means of a look-up table in memory. These are the Aword and Bword respectively. Since each D or Eword (i.e. 10-tuple) appears only in the A or B fragment, never both, it is possible to identify from which fragment the Dword and the Eword comes from. If the Dword and Eword are from the same fragment of the sequence then this implies that there is an error in the DEword and an error signal is sent. If they are not from the same fragment of the sequence, then the absolute position P A can be computed from the Aword and Bword according to the formula as described earlier. The microprocessor 26 then compares P A with P D . If the two positions coincide then the process stops or the process is repeated for a new position P D . If the two positions do not coincide then the process continues until the two values are the same.
  • elements of the software may be implemented in hardware.
  • the first-in-first-out shift register there may be a leading edge detector 58 and a shift register 60 implemented in hardware and arranged as shown in dotted lines in FIG. 3.
  • Such a hardware arrangement has the advantage of speed in some applications.
  • any form of electromagnetic radiation may be adapted to a suitably encoded strip.
  • the coded strip may, in certain embodiments, be in the form of a magnetic tape.

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  • Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Error Detection And Correction (AREA)
  • Signal Processing For Digital Recording And Reproducing (AREA)
  • Compression, Expansion, Code Conversion, And Decoders (AREA)
  • Dc Digital Transmission (AREA)
  • Optical Transform (AREA)
  • Optical Recording Or Reproduction (AREA)
  • Transmission And Conversion Of Sensor Element Output (AREA)
US07/536,678 1988-11-08 1989-11-07 Position encoder using a pseudo-random coding sequence Expired - Lifetime US5173693A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8826114 1988-11-08
GB888826114A GB8826114D0 (en) 1988-11-08 1988-11-08 Decoding of random sequences

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US (1) US5173693A (fr)
EP (1) EP0368605B1 (fr)
JP (1) JP3393134B2 (fr)
AT (1) ATE116080T1 (fr)
DE (1) DE68920123T2 (fr)
GB (1) GB8826114D0 (fr)
WO (1) WO1990005414A2 (fr)

Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1995005707A1 (fr) * 1991-06-06 1995-02-23 Trj & Company Codeur absolu utilisant des signaux analogiques multiphases
US5506579A (en) * 1991-06-06 1996-04-09 Trj & Company Absolute encoder using multiphase analog signals
US5739775A (en) * 1993-07-22 1998-04-14 Bourns, Inc. Digital input and control device
US5841274A (en) * 1997-01-29 1998-11-24 Mitutoyo Corporation Induced current absolute position transducer using a code-track-type scale and read head
US5880683A (en) * 1993-07-22 1999-03-09 Bourns, Inc. Absolute digital position encoder
US6199292B1 (en) * 1998-11-04 2001-03-13 Agilent Technologies Electromechanical dimensioning device
US6294910B1 (en) * 1997-09-26 2001-09-25 The Torrington Company Digital position sensor for sensing position of a moving target
US20020050756A1 (en) * 2000-01-25 2002-05-02 Yoshinori Ito Absolute position detecting device for a linear actuator
US20040046679A1 (en) * 2002-06-28 2004-03-11 Yasuo Nekado Position detection apparatus
US6760682B1 (en) 1999-08-03 2004-07-06 Dr. Johannes Heidenhain Gmbh Position-measuring device
US20060071818A1 (en) * 2002-07-30 2006-04-06 Frank Muller Device for positional and/or length determination
WO2010049049A1 (fr) * 2008-10-30 2010-05-06 Dr Johannes Heidenhain Gmbh Dispositif de mesure de position absolue
US20110128396A1 (en) * 2009-11-27 2011-06-02 Sony Corporation Position detection apparatus, image taking apparatus and position detection method
US20110208475A1 (en) * 2008-10-30 2011-08-25 Dr. Johannes Heidenhain Gmbh Absolute angle coding and angle measuring device
CN106370213A (zh) * 2015-07-24 2017-02-01 赫克斯冈技术中心 绝对位置确定
US9871595B2 (en) 2016-04-27 2018-01-16 Industrial Technology Research Institute Decoding device and method for absolute positioning code
US10115045B2 (en) 2015-09-03 2018-10-30 Hexagon Technology Center Gmbh Absolute surface coding/encoding an area in absolute terms

Families Citing this family (3)

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GB9000097D0 (en) * 1990-01-03 1990-03-07 March Adrian Res Ltd Position sensor
DE102008054042A1 (de) 2008-10-30 2010-05-06 Dr. Johannes Heidenhain Gmbh Absolute Positionscodierung und Positionsmessvorrichtung
CN107525471B (zh) * 2017-08-21 2020-02-04 合肥工业大学 二维绝对式编码三自由度运动平台测量系统

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US4628298A (en) * 1984-06-22 1986-12-09 Bei Motion Systems Company, Inc. Chain code encoder
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US4572952A (en) * 1982-07-28 1986-02-25 Adrian March Research Ltd. Position sensor with moire interpolation
US4631519A (en) * 1982-09-01 1986-12-23 Rosemount Engineering Company Limited Position measuring apparatus
US4628298A (en) * 1984-06-22 1986-12-09 Bei Motion Systems Company, Inc. Chain code encoder
US4780600A (en) * 1986-01-10 1988-10-25 Rosemount Limited Optical displacement transducer
US4914437A (en) * 1986-12-04 1990-04-03 Regents Of The University Of California Encoder for measuring both incremental and absolute positions of moving elements
US4906992A (en) * 1988-02-22 1990-03-06 Dynamics Research Corporation Single track absolute encoder
US4947166A (en) * 1988-02-22 1990-08-07 Dynamics Research Corporation Single track absolute encoder
US4965503A (en) * 1988-03-23 1990-10-23 Tokyo Keiki Co., Ltd. Positional information generating apparatus and code means therefor

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New Pseudorandom Encoding Technique for Shaft Encoders With Any Desired Resolution, Electronic Letters, vol. 23, No. 10, May 7, 1987 (Hitchin, Herts, GB) pp. 507-509.

Cited By (26)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5506579A (en) * 1991-06-06 1996-04-09 Trj & Company Absolute encoder using multiphase analog signals
WO1995005707A1 (fr) * 1991-06-06 1995-02-23 Trj & Company Codeur absolu utilisant des signaux analogiques multiphases
US5739775A (en) * 1993-07-22 1998-04-14 Bourns, Inc. Digital input and control device
US5751230A (en) * 1993-07-22 1998-05-12 Bourns, Inc. Digital input and control device
US5880683A (en) * 1993-07-22 1999-03-09 Bourns, Inc. Absolute digital position encoder
US5841274A (en) * 1997-01-29 1998-11-24 Mitutoyo Corporation Induced current absolute position transducer using a code-track-type scale and read head
US6054851A (en) * 1997-01-29 2000-04-25 Mitutoyo Corporation Induced current absolute position transducer method using a code-track-type scale and read head
US6294910B1 (en) * 1997-09-26 2001-09-25 The Torrington Company Digital position sensor for sensing position of a moving target
US6199292B1 (en) * 1998-11-04 2001-03-13 Agilent Technologies Electromechanical dimensioning device
US6760682B1 (en) 1999-08-03 2004-07-06 Dr. Johannes Heidenhain Gmbh Position-measuring device
US20020050756A1 (en) * 2000-01-25 2002-05-02 Yoshinori Ito Absolute position detecting device for a linear actuator
US6768426B2 (en) * 2002-06-28 2004-07-27 Sony Precision Technology Inc. Position detection apparatus
US20040046679A1 (en) * 2002-06-28 2004-03-11 Yasuo Nekado Position detection apparatus
US20060071818A1 (en) * 2002-07-30 2006-04-06 Frank Muller Device for positional and/or length determination
US7148817B2 (en) * 2002-07-30 2006-12-12 Elgo-Electric Gmbh Device for positional and/or length determination
US20110218761A1 (en) * 2008-10-30 2011-09-08 Dr Johannes Heidenhain Gmbh Absolute position measuring device
US20110208475A1 (en) * 2008-10-30 2011-08-25 Dr. Johannes Heidenhain Gmbh Absolute angle coding and angle measuring device
WO2010049049A1 (fr) * 2008-10-30 2010-05-06 Dr Johannes Heidenhain Gmbh Dispositif de mesure de position absolue
US20110128396A1 (en) * 2009-11-27 2011-06-02 Sony Corporation Position detection apparatus, image taking apparatus and position detection method
US8558721B2 (en) * 2009-11-27 2013-10-15 Sony Corporation Position detection apparatus, image taking apparatus and position detection method
CN106370213A (zh) * 2015-07-24 2017-02-01 赫克斯冈技术中心 绝对位置确定
US10082409B2 (en) 2015-07-24 2018-09-25 Hexagon Technology Center Gmbh Absolute position determination
CN106370213B (zh) * 2015-07-24 2018-12-18 赫克斯冈技术中心 绝对位置确定
US10115045B2 (en) 2015-09-03 2018-10-30 Hexagon Technology Center Gmbh Absolute surface coding/encoding an area in absolute terms
US9871595B2 (en) 2016-04-27 2018-01-16 Industrial Technology Research Institute Decoding device and method for absolute positioning code
US10243668B2 (en) 2016-04-27 2019-03-26 Industrial Technology Research Institute Positioning measurement device and the method thereof

Also Published As

Publication number Publication date
EP0368605A3 (en) 1990-06-27
DE68920123T2 (de) 1995-05-04
WO1990005414A2 (fr) 1990-05-17
GB8826114D0 (en) 1988-12-14
WO1990005414A3 (fr) 1990-06-28
ATE116080T1 (de) 1995-01-15
EP0368605B1 (fr) 1994-12-21
JPH03503825A (ja) 1991-08-22
JP3393134B2 (ja) 2003-04-07
DE68920123D1 (de) 1995-02-02
EP0368605A2 (fr) 1990-05-16

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